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Adding Velocities In SR

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Posted by Alexander on December 18, 2001 01:46:49 UTC

Using symmetry of motion which results in Lorents transformations, one can derive as a mathematical consequence the rule of velocity additions (say, object moving with the velocity v in the moving with the velocity u coordinate system):

(v+u)' = (v+u)/(1+vu/c2).

You may plug u=c and v=c and the result is c. Plugging much less than c velocities results in Newtonian rule: (v+u)'=v+u

If one velocity is c, the result is c regardless the value for the other.

The only case where the equation "breaks down" is when v=c and u=-c (corresponds to the case of calculating of the relative speed of two "catching up" photons moving in the same direction). The equation gives undefined 0/0 value.

Does math suggests that "from the point of wiev of its next-door neighbor" a photon does not exist?

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